1. Field of the Invention
The present invention relates to a rotary body support structure and an image forming apparatus using the same. More particularly, the present invention relates to a structure for positioning a photoconductive drum or image carrier or similar drum included in an image forming apparatus.
2. Description of the Background Art
Generally, a copier, printer, facsimile apparatus or similar image forming apparatus includes a plurality of drums for image formation, e.g., a photoconductive drum or image carrier and a drum included in an image transferring unit. A drum or similar rotary body is usually rotatably mounted on a shaft, i.e., freely rotatable relative to the shaft. Particularly, to facilitate machining and assembly, it is a common practice to prepare a shaft and a rotary body separate from each other and then insert the shaft into the rotary body to allow the latter to freely rotate on the former.
The shaft is, in many cases, mounted to the rotary body after its axis has been positioned, because the shaft determines the axis of the rotary body. Japanese Patent Laid-Open Publication No. 2001-208044, for example, discloses the following assembling procedure. One of end plates mounted on axially opposite ends of a photoconductive drum or rotary body is formed with slots, each being triangular as seen in a front view, at opposite sides of the center. A rotation transmitting member is formed with tapered surfaces capable of mating with the above slots on one of axially opposite sides and formed with a tapered, concave, conical surface on the other side. The rotation transmitting member is mounted to a rotary shaft, which is inserted in the drum, such that the tapered surfaces bite into the slots of the end plate. A knob member is mounted to the shaft with its boss mating with the tapered conical surface and is moved in the axial direction to position the drum in the axial direction. At the same time, the tapered portions mate with each other to match the axis of the drum and that of the rotation transmitting member. Further, when the knob member is mounted to a stationary portion included in an apparatus body, the drum is positioned inside the apparatus body because the knob member has been positioned relative to the axis of the drum.
While the procedure described above matches the axes of the members formed with tapered surfaces by causing the tapered surfaces to mate with each other, the procedure has the following problem left unsolved.
Today, there is an increasing demand for full-color or similar multicolor images as distinguished from single-color images. In this respect, accurately positioning a plurality of photoconductive drums relative to each other is essential for superposing images of different colors in accurate register. The drums, each being assigned to a particular color, each are sometimes mounted on a respective process cartridge or image forming unit together with various process units including a charger, a developing unit and a cleaning unit. In this case, a particular rotary shaft is inserted in each drum cartridge by cartridge.
Although a multicolor image forming apparatus tends to increase in size in accordance with the number of colors, size reduction is a prerequisite. For size reduction, the individual process cartridge and a space available in the apparatus are decreasing. To meet such a demand as to configuration, after the drum has been temporarily positioned, the rotary shaft is inserted into the drum. However, a space available for inserting the rotary shaft is extremely limited. Moreover, a space inside a small-size apparatus does not have a sufficient margin in the axial direction that is necessary for the drum of the document mentioned earlier, among the others, to be prevented from moving in the axial direction, i.e., in the direction of thrust. This is also true when maintenance or replacement must be performed by hand, resulting in extremely inefficient work.